Field of the Disclosure
The present invention relates generally to chemically prepared toner having a core shell structure for use in electrophotography and more particularly to emulsion aggregation chemically prepared toner including a styrene acrylic polyester copolymer used for the shell and process to make the same.
Description of the Related Art
Toners for use in electrophotographic printers include two primary types, mechanically milled toners and chemically prepared toners (CPT). Chemically prepared toners have significant advantages over mechanically milled toners including better print quality, higher toner transfer efficiency and lower torque properties for various components of the electrophotographic printer such as a developer roller, a fuser belt and a charge roller. The particle size distribution of CPTs is typically narrower than the particle size distribution of mechanically milled toners. The size and shape of CPTs are also easier to control than mechanically milled toners.
There are several known types of CPT including suspension polymerization toner (SPT), emulsion aggregation toner (EAT)/latex aggregation toner (LAT), toner made from a dispersion of pre-formed polymer in solvent (DPPT) and “chemically milled” toner. While emulsion aggregation toner requires a more complex process than other CPTs, the resulting toner has a relatively narrower size distribution and improved print resolution.
One important characteristic of any toner is its fuse window. The fuse window is the range of temperatures at which fusing is satisfactorily conducted without incomplete fusion and without transfer of toner to the heating element, which may be a roller, belt or other member contacting the toner during fusing. Thus, below the low end of the fuse window the toner is incompletely melted and above the high end of the fuse window the toner flows onto the fixing member where it mars subsequent sheets being fixed. It is preferred that the low end of the fuse window be as low as possible to reduce the required temperature of the fuser in the electrophotographic printer to therefore improve the printer's safety and to conserve energy.
However in addition to fuse at an energy saving low temperature, the toner must also be able to survive the temperature and humidity extremes associated with storage and shipping—commonly called the ship/storage test. Caking or blocking of the toner during shipping and storage usually results in print flaws. Energy saving low fusing toner is desirable but the low end of the fuse window cannot be so low that the toner melts during the storing or shipping of a cartridge containing the toner. A low melt/low energy fusing toner must be robust to shipping and storage conditions in order to be attractive in a worldwide market. However, many toner formulations cannot simultaneously meet the demand to fuse at low temperatures while also passing the ship/storage tests.
Accordingly, it will be appreciated a core shell toner formulation and process to make the same that can fuse at an energy saving low temperature while passing the ship/storage test is desirable.